Adiabatic Surface Research Articles

Entropy Considerations in Stochastic Electrodynamics

The use of entropy concepts in the field of stochastic electrodynamics is briefly reviewed here. Entropy calculations that have been fully carried out to date are discussed in two main cases: first, where electric dipole oscillators interact with zero-point, or zero-point plus Planckian, or Rayleigh–Jeans radiation; and second, where only these radiation fields exist within a cavity. The emphasis here is on the first, more complicated, case, where both charged particles and radiation fields are present and interacting. Unlike the usual exposition on entropy in classical statistical mechanics, involving probabilistic notions of phase-space occupation, the calculations to date for both particles and fields, or for fields alone, follow the caloric entropy method, where the notions of heat flow, adiabatic surfaces, and isothermal conditions are utilized. Probability notions certainly still enter into the calculations, as the fields and charged particles interact stochastically together, following Maxwellian electrodynamics. Examples of phase-space calculations for harmonic oscillators and classical hydrogen atoms are carried out, emphasizing how much farther caloric entropy calculations have successfully gone.

Assessing and mitigating building fire risk based on the scenario clusters in Bangladesh

The increasing occurrence of fire hazards in residential buildings in Bangladesh has led to severe property damage, physical injuries, and fatalities, underscoring a critical research gap in effective fire risk management. This study aims to address this gap by identifying key fire risks and proposing mitigation strategies using BIM technology. The research employs a comprehensive survey and scenario clustering methodology to identify these risks and assess the efficacy of various fire-resistant materials. Data collection involved questionnaires distributed to 200 respondents, including building owners, occupants, engineers, and firefighters. These clusters are based on the metrics of fatality numbers and property damage to quantify fire risk. Findings highlight the significant role of wall and ceiling lining materials (RII = 0.919) in contributing to fire risk. Further analysis was conducted using a residential building model developed in Autodesk Revit and simulated in Pyrosim software, assessing various lining materials. Quantitative results demonstrated that fire brick is the most effective material, exhibiting the lowest heat release rate (968 kW/m2), minimum adiabatic surface temperature (28°C), minimum heat transfer coefficient (1.75 W/m2/K), and lowest surface burning rate (7.5e−08 Kg/m2/s). These results suggest that fire brick is the optimal choice for enhancing fire resistance in residential buildings.

Emergence of the Molecular Geometric Phase from Exact Electron-Nuclear Dynamics.

Geometric phases play a crucial role in diverse fields. In molecules, they appear when a reaction path encircles an intersection between adiabatic potential energy surfaces and the molecular wave function experiences quantum-mechanical interference effects. This intriguing effect, closely resembling the magnetic Aharonov-Bohm effect, crucially relies on the adiabatic description of the dynamics, and it is an open issue whether and how it persists in an exact quantum dynamical framework. Recent works suggest that the molecular geometric phase is an artifact of the adiabatic approximation, thereby challenging the entire concept. Here, building upon a recent investigation (Martinazzo, R.; Burghardt, I. Phys. Rev. Lett. 2024, 132, 243002), we address this issue using the exact factorization of the total wave function. We introduce instantaneous gauge-invariant phases separately for the electrons and nuclei and use them to monitor the phase difference between the trailing edges of a wavepacket encircling a conical intersection between adiabatic surfaces. The transition from the time-dependent open-path phase differences to the closed-path limit is examined, revealing how the phase differences in the electronic and nuclear subspaces compensate for each other upon path closure. In this way, we unambiguously demonstrate the role of the geometric phase in the interference process and shed light on its persistence beyond the adiabatic approximation.

Surrogate Model-Driven Estimation of Adiabatic Surface Temperature of Fire Exposed Suspension Bridge Towers

Surrogate Model-Driven Estimation of Adiabatic Surface Temperature of Fire Exposed Suspension Bridge Towers

Modeling of Soot Emission in Turbulent Diffusion Flames Impinging on a Cold Surface

ABSTRACT A hydrocarbon flame impinging on a cold surface produces an enhanced soot emission compared to the identical free flame. Cooking with biomass fuels is one practical process where soot emissions due to flame impingement has important environmental and health consequences. This problem was examined in a simplified system in which a turbulent non-premixed ethylene flame impinged on a cold surface. Previous experiment on this configuration examined the influence of a number of parameters on soot emission. The present paper uses numerical modeling to investigate the mechanism of soot emission enhancement in this configuration. Variations in the height of the surface above the fuel jet inlet showed going through a maximum, replicating the data. Since soot behavior can be affected by both thermal quench and flow field disruption, we decoupled the processes by replacing the cold surface with an adiabatic surface. These results indicated that most of the emission enhancement was due to the flow field disruption and not due to thermal quench. The modeling suggests that the presence of the surface changes the scalar dissipation rate, which influences C2H2 concentration, a key species in the soot surface growth process. Specifically, the surface causes a spike in the scalar dissipation rate adjacent to the surface, which significantly influences C2H2 concentration and results in increased soot production. The surface also forces the flame to spread radially, allowing more O2 to penetrate the flame immediately, enhancing the soot oxidation process. The combination of the enhanced soot production and oxidation produces the observed behavior.

High-speed perforation of IN718 plates by spherical TC4 Ti alloy projectiles: Experiments and modeling

Data and knowledge on ballistic performance of Inconel-718 (IN718) alloy is critical for evaluating the resistance of turbine blades against foreign object impacts in aeronautical and astronautical industries. Ballistic perforation experiments (impact velocity 480 ms−1 to 1340 ms−1) with TC4 spherical projectiles (5-mm-diameter) are conducted on IN718 target plates (2-mm-thick) in this work, along with high-speed photography. The IN718 plates show multiple deformation and failure modes (bulging, dishing, petaling and plugging). The ballistic limit velocity for the investigated projectile/target combination is 823 ms−1. Postmortem material characterizations (optical photography, scanned electron microscopy and energy dispersive spectrometry) are conducted on recovered projectiles and bullet hole inner walls, and the observations indicate adiabatic shearing, surface melting and abrasion of projectile material. A finite element model based on the Johnson–Cook constitutive model and failure criterion is established, and reproduces the ballistic experiments. Dimensionless analyses are conducted on the dimensions of postmortem projectiles and bullet holes, and the projectile residual velocity/mass. On the basis of experimental observations and theoretical analysis of the projectile dynamics, the whole perforation process is divided into three stages (the entering, cratering and plugging stages). A multi-stage analytical model on perforation is then developed considering the effects of cavity expansion, projectile deformation and abrasion, and can well predict the projectile dynamics during entering and cratering stages.

The Impact of Roughness and Partitions in Thermal Convection to Enhance the Heat Transport

Abstract In this investigation, we explore the profound impact of adiabatic partitions on heat transport within a square Rayleigh-Bénard (RB) convection enclosure characterized by surface roughness on the lower hot and upper cold plates. The surface irregularities take the form of a rectangular base and a triangular apex. Our study employs two-dimensional direct numerical simulations spanning the Rayleigh number (Ra) range of 106–108 and a Prandtl number (Pr) of 1. Adiabatic partitions, strategically positioned between successive roughness, serve as the focal point of our exploration. Remarkably, our findings reveal a substantial enhancement in heat transport with the introduction of a partition board between consecutive roughness elements. As we escalate the number of partitions from one to four, the heat flux experiences a notable augmentation, reaching 2.3 times that of the classical square RB configuration. This enhancement is attributed to the breakdown of large-scale rolls into multiple rolls, a phenomenon intensified by the increased partition height. Further intriguing observations unfold as we investigate the interplay of surface roughness and partitions. Configurations featuring roughness with partitions exhibit an impressive 2.7 times heat flux enhancement compared to the classical square RB setup. The complex interplay of heat transport improvement is closely connected to optimizing the distance between the conduction plate and the partition. Through meticulous analysis, we identify that the optimal gap facilitates heightened local velocity, effectively thinning the thermal boundary layer and consequently augmenting the overall heat flux. In essence, our study sheds light on the synergistic effects of adiabatic partitions and surface roughness in the context of RB convection. The observed enhancements in heat transport underscore the potential for tailored design strategies involving partitions and surface modifications to optimize thermal performance in diverse applications.

Effect of surface radiation on the stability of hypersonic flat plate boundary layer

Transition of hypersonic boundary layer flow is an important problem in aerodynamic research. To obtain the natural transition position using the flow stability analysis method, it is necessary to analysis the neutral curve and the perturbation growth rule. Accurate calculation of the basic flow is the basis and prerequisite for stability analysis. This paper proposes that surface radiation should be considered in the analysis of hypersonic boundary layer flow stability due to the high temperatures at the vehicle surface caused by aerodynamic heating. In order to obtain the influence of surface radiation on the flow stability, we assume that the surface satisfies the energy balance and the gas satisfies calorimetrically perfect gas properties. To simplify the analysis, gas radiation has been neglected. The boundary layer analysis of a hypersonic flat plate with and without radiation has been performed by a combination of flow stability theory and direct numerical simulation. It is found that high temperature radiation on the surface causes energy to transfer outwards. The results showed that surface temperature decreases along the streamwise direction and is no longer an adiabatic surface temperature. Instability interval decreases and the maximum growth rate increases. The range of the instability region expressed in dimensionless frequency values moves to lower frequency as the Mach number increases. Maximum growth rate shows a tendency to increase and then decrease as the Mach number increases.

Exact solutions based on Segre classification in the f(R) modified theory of gravity

In this article, the Segre classification approach is used to obtain some new solutions for spherically symmetric static spacetime metric corresponding to Segre types [(1, 111)], [1, (111)], [(1, 1)(11)], or [1, 1(11)]. The eigenvalue degeneracy in these situations correlates to timelike and spacelike eigenvectors and their primary null direction, which identify the kind of matter distribution in space and aid in the consideration of novel solutions for the corresponding energy momentum tensor. The isotropic Segre type [(1, 111)] in modified theory provides the Schwarzschild de-Sitter/anti-de-Sitter solutions, whereas in types [1, (111)] and [1, 1(11)] depending upon matter distribution new obtained solutions adhere all the physical conditions and present the viable trends of energy and causality conditions. Moreover, the profiles of the adiabatic index, surface, and gravitational redshift are observed along with the hydrostatic equilibrium using the Tolman–Oppenheimer–Volkoff equation. Additionally, for these types the solution is compared with observational data, and numerical values are calculated for central and surface densities and central pressure of compact star candidates KS1731-260\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$KS 1731-260$$\\end{document} and PSRJ1614-2230\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$PSR J1614-2230$$\\end{document}. Segre type [(1, 1)(11)] relates to a non-null electromagnetic field that corresponds to models with anisotropy in dark energy, which is demonstrated by graphical analysis. Dark energy does not behave as an ordinary matter resulting in the violation of strong energy condition and the causality condition.

ASSESSMENT OF THE MECHANICAL STRENGTH OF A STRUCTURE SUBJECT FO FIRE ATTACK AT THE WILDLAND‐URBAN INTERFACE (WUI)

AbstractFires at the Wildland‐Urban Interface (WUI) have a strong detrimental impact on the built environment. This study evaluates the effect of fire in the WUI on steel sandwich panels in a prescriptive fire field experience. The heat transfer mechanisms are obtained using a computational fluid dynamic (CFD) simulation, more specifically the adiabatic surface temperatures (AST) of the structure. The ASTs were applied in a finite element model (FEM) as boundary conditions in the thermal field in order to quantify the heat transfer processed by the FEM. In conclusion, it is identified which area of the structure is most affected due to the temperatures in the panels.

Parametrically Managed Activation Functions for Improved Global Potential Energy Surfaces for Six Coupled 5A' States and Fourteen Coupled 3A' States of O + O2.

We report new potential energy surfaces for six coupled 5A' states and 14 coupled 3A' states of O3. The new surfaces are created by parametrically managed diabatization by deep neural network (PM-DDNN). The PM-DDNN method uses calculated adiabatic potential energy surfaces to discover and fit an underlying adiabatic-equivalent set of diabatic surfaces and their couplings and obtains the fit to the adiabatic surfaces by diagonalization of the diabatic potential energy matrix (DPEM). The procedure yields the adiabatic surfaces and their gradients, as well as the DPEM and its gradient. If desired one can also compute the nonadiabatic coupling due to the transformation. The present work improves on previous work by using a new coordinate to guide the decay of the neural network contribution to the many-body fit to the whole DPEM. The main objective was to obtain smoother potentials than the previous ones with better suitability for dynamics calculations, and this was achieved. Furthermore, we obtained suitably small deviations from the input reference data. For the six coupled 5A' surfaces, the 60,366 data below 10 eV are fit with a mean unsigned error (MUE) of 49 meV, and for the 14 coupled 3A' surfaces, the 76,733 data below 10 eV are fit with an MUE of 28 meV. The data below 5 eV fit even more accurately with MUEs of 37 meV (5A') and 20 meV (3A').

Enhancing Heat Storage Cooling Systems via the Implementation of Honeycomb-Inspired Design: Investigating Efficiency and Performance

This study presents a novel approach inspired by the hexagonal honeycomb structure found in nature, leveraging image processing algorithms to precisely define complex geometries in thermal systems. Hexagonal phase change material containers and thermally conductive fins were meticulously delineated, mirroring the intricate real-world designs of honeycombs. This innovative methodology not only streamlines setup processes but also enhances our understanding of melting dynamics within enclosures, highlighting the potential benefits of biomimetic design principles in engineering applications. Two distinct honeycomb structures were employed to investigate their impact on the melting process within cavities subject to heating from the left wall, with the remaining walls treated as adiabatic surfaces. The incorporation of a thermally conductive fin system within the enclosure significantly reduced the time required for a complete phase change, emphasizing the profound influence of fin systems on thermal design and performance. This enhancement in heat transfer dynamics makes fin systems advantageous for applications prioritizing precise temperature control and expedited phase change processes. Furthermore, the critical role of the fin system design was emphasized, influencing both the onset and location of the final point of melting. This underscores the importance of tailoring fin systems to specific applications to optimize their performance. Our study highlights the significant impact of the Rayleigh (Ra) number on the melting time in a cavity without fins, revealing a decrease from 6 to 0.4 as the Ra increased from 102 to 105; the introduction of a fin system uniformly reduced the melting time to Ste.Fo = 0.5, indicating fins’ universal effectiveness in optimizing thermal dynamics and expediting the melting process. Moreover, the cavity angle was found to significantly affect the fluid fraction diagram in unfanned cavities but had minimal impact when fins were present, highlighting the stabilizing role of fins in mitigating gravitational effects during melting processes. These insights expand our understanding of cavity geometry and fin interactions in heat transfer, offering potential for enhanced thermal system designs in various engineering applications. Decreasing thermal conductivity (λ) by increasing the fin thickness can halve the melting time, but the accompanying disadvantages include a heavier system and reduced energy storage due to less phase change material, necessitating a careful balance in decision-making.

ANT 2023: A program for adiabatic and nonadiabatic trajectories

ANT 2023 is a program for quasiclassical and semiclassical trajectories, both single-surface trajectories for which the Born-Oppenheimer approximation is valid and multi-surface calculations with electronic state changes, i.e., for electronically adiabatic and electronically nonadiabatic trajectories. There are several methods available for multisurface problems: surface hopping with or without time uncertainty and with or without decoherence, semiclassical Ehrenfest, self-consistent decay of mixing, and coherent switching with decay of mixing (CSDM). The potential surface for single-surface problems may be an analytic potential function supplied by the user, or one may use direct dynamics. To use the adiabatic representation (i.e., electronically adiabatic basis functions) for electronically nonadiabatic dynamics, the user may either provide the adiabatic surfaces and nonadiabatic couplings by direct dynamics, or the program may calculate them from diabatic surfaces and diabatic couplings, which are usually analytic. One can also use analytic fits to the surfaces and couplings to carry out calculations entirely in the diabatic representation. The curvature-driven approximation is available as an option for use with CSDM and trajectory surface hopping. The ANT 2023 program is especially recommended for calculations with analytic potential energy surfaces and couplings because of its high efficiency for such calculations. Program SummaryProgram Title: ANT 2023, revision BCPC Library link to program files:https://doi.org/10.17632/gr74wwckcp.1Developer's repository link: https://doi.org/10.5281/zenodo.10011563Licensing Provisions: Apache-2.0Programming language: Fortran 90Interfaces to other programs: For direct dynamics, the code has well tested interfaces to the Gaussian 09 [1], Gaussian 16 [2], MOPACmn [3], and Molpro [4] electronic structure codes. The interfaces are included, but these electronic structure programs must be obtained separately. Users may also provide their own interfaces to other electronic structure programs.[1] M. J. Frisch et al. Gaussian 09, Gaussian, Inc., Wallingford CT, 2016.[2] M. J. Frisch et al., Gaussian 16, Gaussian, Inc., Wallingford CT, 2016.[3] J. J. P. Stewart et al., MOPAC 5.022mn, University of Minnesota, Minneapolis, MN, 2015; Zenodo. https://doi.org/10.5281/zenodo.8153079[4] H.-J. Werner et al., J. Chem. Phys. 152 (2020) 144107.Nature of problem: classical, quasiclassical, or semiclassical molecular dynamics for electronically adiabatic or electronically nonadiabatic collisions and unimolecular processes of atoms, molecules, and clustersSolution method: The program integrates the classical or semiclassical equations of motion for the motion of the nuclei. ANT 2023 can use anharmonic initial-state selection for initial states of diatomics or harmonic initial-state selection for general polyatomics. The equations of motion for electronically adiabatic processes are Hamilton's equations with potential energy functions corresponding to the Born-Oppenheimer approximation. The equations of motion for electronically nonadiabatic processes (non-Born-Oppenheimer processes) include trajectory surface hopping (fewest switches with or without time uncertainty and with or without decoherence) or several possible mean-field methods, including the semiclassical Ehrenfest method (also called the time-dependent Hartree method), self-consistent decay of mixing, and coherent switching with decay of mixing. Electronically nonadiabatic processes may be treated using either the adiabatic representation or a diabatic representation, and the potential surfaces and couplings may be obtained from analytic fits in a user-supplied subroutine or by direct dynamics, which involves requesting energies, gradients, and couplings as needed from a quantum chemistry electronic structure program. In the adiabatic representation, the coupling may be nonadiabatic coupling vectors (based on gradients of electronic wave functions), time-derivative couplings (based on overlaps of electronic wave functions), or curvature-driven couplings (based on the curvatures of the adiabatic potential energy surfaces).Additional comments: The ANT 2023 program authors are Y. Shu, L. Zhang, J. Zheng, Z. H. Li, A. W. Jasper, D. A. Bonhommeau, R. Valero, R. Meana-Pañeda, S. L. Mielke, Z. Varga, and D. G. Truhlar [5]; the authors of the article [6] describing ANT 2023 are Y. Shu, L. Zhang, and D. G. Truhlar.

PotLib 2023: New version of a potential energy surface library for chemical systems

POTLIB is a library of global and semiglobal potential energy surface subprograms. The library currently features 410 entries, including both single-state entries and multi-state entries. When one calls the routine of a single-state entry, it returns the ground-electronic-state adiabatic potential energy surface at the input geometry. In addition, some entries also return the gradient of the surface. When one calls a multi-state entry, it returns a diabatic potential energy matrix (DPEM). If the entry also has the gradient of the DPEM, one can compute adiabatic surfaces, their gradients, and the nonadiabatic coupling vectors (NACs) from the DPEM and its gradient by diagonalization. Some but not all the routines conform to one of a set of standard interfaces. The goal is to facilitate chemical dynamics research by collecting and disseminating a comprehensive collection of state-of-the-art potential energy routines (developed by a wide, international group of researchers) with systematic and well-defined interfaces for use with chemical dynamics programs. Systems in the library include CHArO2, CHN2O+, CH2O, CH2O2, CH3N2, CH3O, CH4, CH4Br, CH4Cl, CH4F, CH4O, CH4OCl, CH4OF, CH4OH, CH5, CH5+, CH5N, CH5O2, CH8O2, C2H2N2O, C2H2O, C2H4N, C2H4O4, C2H6Cl, C2H6F, C2H6H, C2H6O, C2H6OH, C2H7, C2O2, C3H4O2, C3H7NO, C6H6O, C6H6S, C7H8S, HBrCl, HCl2, HF2, HI2, HLiF, HNaF, HO2, HO3, HOBr, HSiO, H2Br, H2ClO, H2F, H2F2, H2FO, H2Na, H2O, H2O2, H2OBr, H3, H3Cl, H3ClN, H3ClO, H3N, H3O, H3O2, H3+, H3S, H4ClSi, H4N, H4NO, H4O2, H5GeO, H5Si, H7+, AlmHn, Aln, ArNO, K2Rb2, NO2, N2O, N2O2, N3, N4, O3, and O4. New version program summaryProgram title: PotLib 2023CPC Library link to program files:https://doi.org/10.17632/chxxhnnt4p.1Licensing provisions: Apache 2.0Programming language: FortranDoes the new version supersede the previous version?: YesJournal references of previous versions: Comput. Phys. Comm. 144 (2002) 169–187 [1]; Erratum: Comput. Phys. Comm. 156 (2004) 319–32.Nature of problem: Within the Born–Oppenheimer approximation, the electronically adiabatic interactions of atoms and molecules can be represented by a potential energy surface (PES) that depends on the geometry of the reacting species [2-4]. An electronically nonadiabatic system can be approximately described by a diabatic potential energy matrix (DPEM) that also depends on molecular geometry [5,6]. The library contains Fortran subroutines of PESs and DPEMs for reactive and non-reactive systems.Solution method: The user can incorporate a PES, DPEM, or PES set from a DPEM into a chemical dynamics computer code to supply the needed potential or potentials and optionally the gradients (forces) and surface couplings.Summary of revisions: The new version includes many more potentials than the original version of the library.

Numerical study of the convective heat transfer coefficient for steel column surrounded by localized fires

The convective heat transfer coefficient hc characterizes the heat transfer capacity between the fluid-solid interface in a thermal convection phenomenon. At present, values adopted from specifications are mostly used to define the hc coefficients in localized fire researches. In this paper, the specific scenario of the steel column surrounded by fire plume is selected as a typical case to explore the surface hc change rules of the steel column under the action of the fire source at the bottom. Different from the application of the concept of adiabatic surface temperature (AST) to achieve fluid-solid thermal coupling, this paper takes the scenario with the fire source heat release rate (HRR) being 81 kW as an example and conducts a two-way coupling simulation analysis of the fire and the thermal models by means of CFD codes. First, the validity of this simulation methodology is verified by comparing the results of the numerical model and the experiment. Following this, the distribution laws of the spatial velocity and temperature fields are analyzed, and the hc coefficient of the steel column surface is explored in detail using theoretical formula and traditional empirical formula respectively. It is noted that the hc results obtained based on theoretical formula can comprehensively consider the velocity boundary layer and temperature boundary layer situations above the column surface, which is a direct result of the definition of the convective heat transfer coefficient. It is found that the hc‾ is lower at the bottom of the column and increases with height, with relative maximum value in the lower and middle parts of the column, reaching around 40 W/m2 K. The hc‾ results decrease along the axial direction, with the value of upper part of the column being about 20 W/m2 K. In contrast, the hc‾ distributions along the height obtained by the empirical formulas are similar to the distribution of fire plume velocity along the height. In other words, it considers only the effect of the velocity boundary layer, while the effect of significant changes in fluid temperature on convective heat transfer behavior is less considered. Compared to the results based on the theoretical definition, the hc‾ results obtained by empirical formulas are significantly smaller in the lower and middle parts of the column, and higher at the top of the column. Finally, a new hc‾ practical formula for the column surfaces surrounded by fire plume is proposed, which agrees well with the results based on the theoretical definition in several cases.

Fire exposure measurements using plate thermometers

AbstractPlate thermometers (PT) are known and utilized in fire testing for more than 30 years. They are simple devices that measure the temperature of the thin plate, made of a thermal conductor, that is exposed to fire from one side and insulated from the opposite side. The main advantage of measuring thermal exposure using a plate thermometer is its ability to capture both the convective and radiative parts of the heat flux. However, thermal exposure is not directly the value the plate thermometer outputs. For this reason, an adiabatic surface temperature (AST), which could be considered as an objective measure of thermal exposure, can be calculated on the basis of the plate thermometer output. In this work, the abilities for fire‐exposure measurements using plate thermometers are discussed.This work introduces the closed‐form analytical solution of the plate thermometer heat balance equation for an adiabatic surface temperature. The authors consider the introduced solution as the best method, at this moment, for the evaluation of AST based on the PT output. This allows several findings to be presented that are not affected by the shortcomings of previously used methods for the AST evaluation.

Thermo-mechanical behavior of composite beams with corrugated steel webs exposed to localized fire

In this study, a one-way coupling methodology combining fire simulation based computational fluid dynamics (CFD) with finite element (FE) analysis is proposed to investigate the thermo-mechanical behaviors of composite beams with corrugated steel webs (CSWs) under localized fire exposure. Fire Dynamics Simulator (FDS) is used to simulate the local fire environment, and the adiabatic surface temperature (AST) data obtained in FDS are imported into the FE models in ABAQUS by the fds2ascii coupling tool. The validations of FDS models and the CFD-FE coupling method are verified by a localized fire test on a steel beam conducted by the National Institute of Standards and Technology (NIST). Then, the CFD-FE coupling method is applied to analyze the thermo-mechanical behaviors of composite beams with concrete flanges and CSWs exposed to localized fire. As the fire exposure time increases, the composite beam appears significant variation of the temperature gradient at elevated temperature, and induce the dynamic, uneven temperature field in the structural members. Due to the influences of the temperature gradient field, the traditional design assumptions for composite beams with CSWs are not valid when the structures suffered a localized fire. It found that the shear stress on the CSWs is no longer evenly distributed along the depth at elevated temperatures, and the concrete flange resists a considerable part of the sectional shear force, particularly of the fire-affect zone. This study hopes to provide a basis for the fire resistance design of composite girder bridges with CSWs.

Semiclassical Multistate Dynamics for Six Coupled 5A' States of O + O2.

Dynamics simulations of high-energy O2-O collisions play an important role in simulating thermal energy content and heat flux in flows around hypersonic vehicles. To carry out such dynamics simulations efficiently requires accurate global potential energy surfaces and (in most algorithms) state couplings for many energetically accessible electronic states. The ability to treat collisions involving many coupled electronic states has been a challenge for decades. Very recently, a new diabatization method, the parametrically managed diabatization by deep neural network (PM-DDNN), has been developed. The PM-DDNN method uses a deep neural network architecture with an activation function parametrically dependent on input data to discover and fit the diabatic potential energy matrix (DPEM) as a function of geometry, and the adiabatic potential energy surfaces are obtained by diagonalization of a small matrix with analytic matrix elements. Here, we applied the PM-DDNN method to the six lowest-energy potential energy surfaces in the 5A' manifold of O3 to perform simultaneous diabatization and fitting; the data are obtained by extended multistate complete-active-space second-order perturbation theory. We then used the adiabatic surfaces for dynamics calculations with three methods: coherent switching with decay of mixing (CSDM), curvature-driven CSDM (κCSDM), and electronically curvature-driven CSDM (eκCSDM). The κCSDM calculations require only adiabatic potential energies and gradients. The three dynamical methods are in good agreement. We then calculated electronically nonadiabatic, electronically inelastic, and dissociative cross sections for seven initial collision energies, five initial vibrational levels, and four initial rotational levels. Trends in the electronically inelastic cross sections as functions of the initial collision energy and vibrational level were rationalized in terms of the coordinate ranges where the gaps between the second and third potential energy surfaces are small.

Performance of steel cable-stayed bridges in ship fires, part I: Numerical method and baseline fire scenario study

Over the past decade, the previous hysteretic recognition of the fire threat to bridges has provoked significant progress in understanding the fire performance of bridges. However, despite the growing maritime shipment of combustibles, scarce studies have contributed to evaluating the safety of steel cable-stayed bridges subjected to under-girder ship fires. Limited existing knowledge is still based upon the less precise temperature curve method and flame geometry modeling. This study developed an advanced numerical method to more accurately evaluate the response of steel cable-stayed bridges subjected to ship fires. First, the computational fluid dynamics (CFD) approach was used to reproduce realistic fire conditions. An efficient thermal boundary, adiabatic surface temperature, was then transferred to the thermal finite element model of affected girder segments for calculating the temperature propagation. Lastly, this paper used the multiscale structural finite element method to incorporate the local performance variation of exposed girders into the response of the entire bridge. The proposed method was validated by predicting a thermomechanical response of the steel beam exposed to realistic underneath fires, agreeing well with the data from two large-scale structural fire experiments by NIST. Based on the method, the response of a typical steel cable-stayed bridge subjected to ship fires was simulated. Results show that fires can introduce local damage to the girder segments above the fire and alter the internal force distribution of the entire bridge. The bending moment of the girder sections over the fire significantly increases, and the flexural characteristic of pylons is also altered. Both thermal convection and radiation contribute to the temperature increment, and the latter dominates at the locations above fires. Adopting temperature curves can overestimate or underestimate the fire impact, introducing uncertainties to the safety of steel cable-stayed bridges in ship fires and can cause unrealistic stress concentration on the border of heated and unheated domains of exposed floors. The developed advanced method is more competent in capturing the inhomogeneous temperature and stress distribution.

Compact Bardeen Stars in f(R,T)$f(\mathcal {R}, T)$ Theory with Conformal Motion

AbstractA set of exact spherically symmetric solutions for describing the interior of a relativistic star in the context of modified theory of gravity is presented. The existence of a Conformal Killing Vectors (CKV) and Bardeen's model to find the boundary conditions as an exterior space‐time geometry to achieve the metric potentials for current study is used. Moreover, matching conditions have been employed to obtain a set of free parameters for the physical analysis. Furthermore, some physically valid attributes like the behavior of energy density, pressure, equilibrium conditions, the adiabatic index, mass‐radius relation, surface red‐shifts, and compactness factor for the realistic stars such as , , , , and are investigated. It is observed that for the current investigation, the derived compact star solutions are physically acceptable and authentic in the presence of charge with conformal motion.